1. Field of the Invention
The present invention provides a method of checking and correcting a mask pattern, and more particularly, to a method of using an orientation model to sort all edges of a mask pattern into different situations, and then performing the checking and correcting to all situations one by one.
2. Description of the Prior Art
In semiconductor fabrication, lithography process is an important step to transfer an integrated circuit layout to semiconductor wafers. Generally, a wafer manufacture company designs a mask layout according to an integrated circuit layout; and then fabricates a mask having the designed mask layout. Afterwards, by virtue of lithography processes, the pattern on the mask (i.e. the mask pattern) is transferred to a photoresist layer on the surface of a semiconductor wafer in a specific scale.
As the complexity and integration of integrated circuit continue to progress, the size of every segment of a mask pattern is designed smaller. However, the critical dimension (CD) of every segment fabricated by exposures is limited to the resolution limit of the optical exposure tool while transferring the mask pattern. One problem that easily arises during the exposures of a mask pattern with high-density arranged segments to form a pattern on a photoresist is optical proximity effect. Therefore, the resolution loss occurs because of overexposure or underexposure, so as to bring a deviation of the pattern on the photoresist from the original mask pattern. Many saving methods have been used for improving the deviation caused from the optical proximity effect in order to improve the quality of the transferred pattern. The most popular method is optical proximity correction (OPC). And there have been a variety of commercial optical proximity correction software, which can correct the mask pattern theoretically to acquire more correct pattern on a wafer.
A mask pattern corrected by the optical proximity correction must be inspected by a process rule check (PRC) to confirm the correctness of the mask pattern. If the corrected mask pattern completely obeys the rules of the process rule check, the mask pattern is then outputted and provided for lithography process. Inversely, if a portion or all portions of the mask pattern violates the rules of process rule check, the mask pattern needs to be re-modified. The process rule check (PRC) inspects line ends and corners of each segment of a mask pattern to verify that if those geometrical patterns obey the limitation of the critical width and the critical space of the designed integrated circuit layout.
However, the modifying methods of typical optical proximity correction software do not completely take into account the rules of critical width and critical space, resulting in repeated steps of optical proximity correction and process rule check. Therefore, the output of a mask pattern is delayed; and the loading of computer resources is also increased. Sometimes, judgments from those of professional skill in the art are needed to overcome the problems described above, so as to waste the human resources.
During the repeated steps of optical proximity correction and process rule check, each optical proximity correction would modify the mask pattern base on the previous result of process rule check. However, currently process rule checks, which only inspect the geometrical pattern of line ends and corners of the mask pattern, can no longer keep up with the progressing of the complexity and integration of the integrated circuit. Therefore, the deviation from original designed layout can be found only after outputting the mask pattern and after the exposure of lithography processes to form the pattern on the wafers, so as to fabricate the mask over again. And the fabrication cost is greatly increased. Accordingly, a method of checking and correcting mask pattern is provided to improve upon the deficiencies from the prior art.